1. Field of the Invention
This invention relates to an improvement in beneficiating mineral ores, especially phosphate ores. More particularly, the invention relates to a method and apparatus for separating and enriching mineral values from mineral ores.
2. Description of Prior Art
Mineral-containing ores, such as phosphate ores, are usually concentrated or beneficiated in a series of operations which results in a product having a higher content of the desired mineral than the original ores. A commonly accepted criterion of the quality of the product of the beneficiation process is "grade" of the product which, in the case of a phosphate ore, is expressed as % BPL. % BPL is a measure of phosphate, P.sub.2 O.sub.5, content with the amount of the phosphate being calculated from the equation: % P.sub.2 O.sub.5 =% BPL.times.0.4576. In the case of phosphate ore, it is normally desirable to obtain a product containing at least 70% BPL, with the minimum number of processing steps and therefore at a minimum cost.
In prior art, many minerals were beneficiated in complex operations requiring multiple flotation systems. For example, in the case of phosphate ore, the ore was first mined and then slurried with water to form an aqueous slurry. The slurry was then transported, by any suitable means, e.g., a pipeline, to a beneficiation plant wherein the ore was screen to remove relatively large size particles (e.g., larger than 3/4 inch). The undersized ore, in the aqueous pulp form, was subjected to several screening, washing, cyclonic and hydrosizing operations. Two separate fractions of the phosphate ore, one having the particle size range of -20 to +35 and the other of -35 to +150 mesh, commonly referred to as the coarse and the fine "flotation feed", respectively, were subjected to two separate but similar conditioning and flotation steps for further upgrading. As used herein, the term "mesh size" or "mesh" refers to standard Tyler screen mesh sizes.
In the conditioning step, the flotation feed was first contacted with chemicals, i.e., a base, a fatty acid and a hydrocarbon oil, e.g., a fuel oil, which enhanced, in a downstream flotation step, commonly called "rougher flotation", the flotation of the desired phosphate particles from the silica gangue. The phosphate product of the rougher flotation step contained some silica which had to be removed in a second flotation step, commonly called "cleaner flotation", with different chemicals from those used in the rougher flotation. The rougher flotation phosphate product was first treated with a mineral acid, e.g., sulfuric acid, and washed to remove the rougher flotation chemicals. The washed product was then treated with chemicals, e.g. an amine and kerosene, and then subjected to the cleaner flotation, wherein the residual silica was removed from the phosphate-containing product. The above-described combination of sequentially-conducted rougher and cleaner flotation steps will be referred to hereinafter as a "multiple step or two-step flotation process," usually conducted in Denver Flotation Cells. McTaggart, U.S. Pat. No. 1,744,785, Booth, U.S. Pat. No. 2,182,442, and Daman, U.S. Pat. No. 2,651,413, disclose such multiple step flotation processes for mineral ores. Hefner, Jr., U.S. Pat. No. 4,172,029, and Lilley, U.S. Pat. No. 4,440,636, disclose improvements in such conventional, multiple step flotation process. The entire contents of the aforementioned patents are incorporated herein by reference.
It was also proposed in prior art to use vertical flotation columns to separate minerals from other particulate material by froth flotation. Such flotation columns usually employed a plug flow process or utilized a relatively quiescent body of liquid to separate mineral values from non-desirable particulate material. For example, Hollingsworth, U.S. Pat. No. 3,298,519, discloses a vertical flotation column for concentrating minerals in a plug flow process. The process comprises establishing a vertical column of liquid, introducing air into the column, and introducing a mixture of particles of minerals and non-floatable particles into the column at least about two feet below the upper surface of the liquid column.
Hollingsworth, U.S. Pat. Nos. 3,371,779, 4,287,054 and 4,431,531, also disclose vertical flotation columns for concentrating mineral values. In these columns, relatively quiescent operating conditions, which may be facilitated by the presence of baffles, are maintained during the mineral beneficiating processes.
It is a primary object of the present invention to provide an improved process for recovering mineral values from mineral ores.
This and other objects of the invention will become apparent to those skilled in the art from the following description thereof.